The removal of nutrients (nitrogen and phosphorous) from industrial and domestic water/wastewater is an environmental objective of importance. The water industry has a high demand for efficient, reliable, cost-effective and compact technologies to remove lame concentrations of nutrients in water/wastewater. Although, there are various nutrient removal technologies, their use is limited because of their high construction area, capital costs, controls complexity and operational costs of sludge recycle. Furthermore, they must meet strict performance criteria like:                Very low effluent concentrations        Low power consumption        Minimum chemical addition        Low environmental impact        Small construction space        Low sludge production        
The leading nutrient removal processes, are biological. The conventional biological method for ammonia removal is based on two steps:                1. Microbial oxidation of ammonia to nitrate (Nitrification), and        2. Microbial reduction of nitrate to free nitrogen (Denitrification).        
Nitrification is the biological oxidation of ammonium (NH4+) to nitrate (NO3−) through a two-step process which involves:
Step 1: Ammonia Oxidizing Bacteria (AOBs) convert NH4+ to NO2+, and
Step 2: Nitrite Oxidizing Bacteria (NOBs) oxidize NO2− to NO3− AOBs (i.e. Nitrosomonas europaea) are responsible for the first process in nitrification. The reaction is shown below:NH4++3/2O2→NO2−+2H++H2ONOBs (i.e. Nitrobacter) complete the second step in nitrification:NO2−+1/2O2→NO2−
NO3− formed through nitrification is used by plants as a nitrogen source for cellular synthesis or is reduced to N2 through the process of denitrification by heterotrophic bacteria. NO3− can, however, contaminate groundwater if it is not used for synthesis or reduced through denitrification. Heterotrophic bacteria in the absence of free oxygen in water utilize the oxygen attached in NO3− molecule. The reaction by denitrifying bacteria is:NO3−+Organic Matter→N2+CO2+OH−+H2O
In 1999 a remarkable microbial process was identified in Delft University of Technology (The Netherlands). This biological process known by the abbreviation of Anammox (Anaerobic Ammonium Oxidation) occurs in many natural ecosystems where NO2− and NH4+ react into free nitrogen (N2). The bacteria mediating this process belong to the bacterial phylum of Planctomycetes. it is estimated that over 50% of the N2 produced in the oceans is caused by Anammox bacteria. The application of this process is a radical departure from conventional biological nitrification/dentrification and owes its extraordinary interest to the unique features of Anammox bacteria including the oxidation of NH4+ in the absence of oxygen. This characteristic makes Anammox especially attractive both environmentally and economically.
The widely reported slow microbial growth of Anammox and the highly complex intracellular processes are important operating obstacles for the design of processes based on Anammox kinetics. The Anammox processes has an innumerable number of applications in water and wastewater treatment, the food industry, the chemical and petrochemical industries. the mining industry, and in the industrial activities associated with the generation of excess nutrients.
The Anammox process requires partial nitrification so that sufficient concentration of NO2− is available for the Anammox bacteria. Therefore, the overall process consists of two steps. The first step is partial nitrification where NH4+ is partially nitrified to NO2− by AOBs.4NH4++3O2→2NH4++2NO2−+4H++2H2OThe second step is the Anammox process in which NH4+ and NO2− are converted to N2 by Anammox bacteria.NH4++NO2−→N2+2 H2OPartial nitrification and the Anammox process can take place in one reactor where two guilds of bacteria form compact granules. The following equation illustrates a combined partial nitrification and Anammox process.NH4++1.32NO2−+0.066HCO3−+0.13H+→0.26NO3−+1.02N2+0.066CH2O0.5N0.15+2.03H2O
The kinetics and interaction of Anammox with other microbial species like Phosphorous Accumulating Organisms (PAOs) is largely unknown which makes very unreliable the design of BNR processes and reactors. The Anammox process and biological phosphorus removal process have been hitherto developed in separate bioreactors.
The biological phosphorus removal entails the application of PAOs. PAOs were identified by Fuhs and Chen in 1975. The subsequent application of PAOs by J. Barnard in South Africa to remove lame amounts of phosphorus (EBPR-Enhanced biological phosphorous removal) from wastewater, expanded with the Bardenpho process the field of biological nutrient removal. Because chemical salts were not necessary, operating costs were substantially reduced, as were the handling costs of excessive sludge production. One of the drawbacks of EBPR processes is the large number of reactors used, and the construction area required. Furthermore inadequate mixing makes EBPR processes difficult to monitor and control (Alvarez Cuenca and Reza. US Patent Publication No. US-2012-0031836-A1).